The invention relates to a method for location updating in a cellular radio network comprising a home location register for permanently storing location and subscriber data on subscriber mobile stations registered with the network, the geographic coverage area of the network being divided into smaller service areas each comprising a mobile services switching center and a visitor location register for temporarily storing subscriber data on mobile subscriber stations currently located within said service area; the geographic coverage area of each service area being further divided into location areas comprising cells, each of which incorporates at least one fixed radio station capable of establishing a radio link with the active subscriber mobile stations currently located in the cell, the network comprising base stations and subscriber mobile stations in a first system, said subscriber mobile stations automatically informing the network of their location area via base stations to update location data, and base stations and mobile stations in a second system, the mobile stations not automatically informing the network of their location.
Cordless telephone (CT) systems, such as the digital cordless telephone system CT2, have recently come out on the market. Such a system comprises a base station, which is always based on access to an existing fixed telephone network. There are three main types of base stations: a residential base station, a base station connected to a private branch exchange (PBX) in an office or operating independently as a PBX, and telepoint base stations, from which only outbound calls are possible for a CT telephone.
Since the present-day CT systems are regarded as PSTN subscriber connections (access points), a call is addressed to the CT terminal equipment in the normal way by dialing a telephone number in accordance with the PSTN numbering scheme. On the basis of the telephone number, the PSTN then routes the call to a respective subscriber connection to which the CT residential base station or the PBX of the CT office base station is connected. The base station pages the CT terminal equipment over the radio path by means of an identity code determined by the numbering scheme of the CT system, and sets up a call when the terminal equipment responds. In practice, it is thus possible to make a call to the CT terminal equipment only through its residential or office base stations (through predetermined subscriber connections).
Accordingly, the numbering schemes of the present CT systems serve only the CT radio link and are not utilized anywhere in the PSTN.
In the future, it may become advantageous to be able to connect CT systems even to mobile radio networks. As there are no addressable access points (such as PSTN subscriber connections) but only traffic channels used commonly by mobile subscriber equipment, the communication setup is always based on the use of an identity code assigned to the subscriber equipment.
Problematic for the integration of the CT system and the mobile phone system are for example their different numbering schemes and authentication procedures. Solutions to these problems have been disclosed in the Applicants' earlier Finnish patent applications FI910211 and FI920792 (unpublished on the filing date of the present application).
In a cellular radio network, the subscriber can roam freely within the radio coverage area of the network, in which event the network must have information on the location of the subscriber equipment in order that a call to the subscriber may be set up. In the present cellular radio networks, location updating is based on automatic location updating carried out by the subscriber equipment while roaming within the area of the network. In call setup, the subscriber equipment is paged only in the area within which it has communicated to be located last. However, for instance the CT system has no specification of any automatic location updating carried out by the subscriber equipment, and therefore there is no certainty of the location of the subscriber equipment in the network. The valid location information has usually been received in connection with the last call. Thus the setup of an inbound call to such a subscriber similarly as to a normal subscriber to the mobile telephone network would often lead to failure of call setup.
A slight relief to the problem presented by the inaccuracy of location data is offered by the mobile phone system disclosed in EP Patent Application 454 647, in which paging of the mobile telephone and setup of a radio link with the mobile telephone is performed before the call is routed through the network to the mobile telephone. If the paging does not reach the mobile telephone, the call is not routed at all, which reduces needless use of the resources of the transmission network. The paging of the mobile telephone can be performed, besides the area of the exchange in which the mobile telephone is located according to the location data, also within the area of exchanges neighboring the exchange. Such extended paging can be initiated immediately, or it can be proceeded to when the first paging attempt in the primary service area fails. However, in the case of the CT system, this solution leads substantially often to the use of additional paging and thereby to extended call setup times.